1. Field of the Invention
The present invention relates to a diamond interconnection substrate and a manufacturing method therefor, and more particularly to those applicable to a high-power electronic circuit substrate including a high power microwave circuit, which is a diamond circuit substrate, also serving as a heat sink, having multi-layer interconnections.
2. Description of the Background Art
Diamond is a material having the highest thermal conductivity of all materials, in a high temperature range between a room temperature and 200xc2x0 C. Such a property is considered to be important for a heat sink required for lowering temperature of electron devices having, year by year, higher performance and greater heat-releasing values. Conventionally, when utilized as a high-performance heat sink, diamond may be provided with an interconnection of only one layer formed on the surface of the diamond. Thus, a conventional diamond interconnection substrate has attained only one layer of interconnection.
However, when a number of elements are formed on the diamond substrate, the interconnections may cross with each other in the only one interconnection layer. Further, miniaturization of a device may possibly make an interconnection thinner, which will require the interconnection to be electrical power resistant.
Currently, ceramics and conductors are used for circuit substrates, and a combination of simultaneously calcinable Al2O3/W, AlN/W or the like are selected as materials therefor. Some circuit substrates are designed to utilize CuW material, a low-temperature calcinated substrate and so forth, to be divided into a heat radiating portion and a multi-layer interconnection portion. Further, a multi-layer interconnection substrate of BeO is being contemplated in a field where both a highly thermal conductive material and a multi-layer interconnection technique are required.
However, such a circuit substrate had problems in that the thermal conductivity is lower compared to that of diamond, its structure is more complicated and its manufacturing process is troublesome.
It is an object of the present invention to provide a technique by which multi-layer interconnections can be realized using a diamond substrate with the highest thermal conductivity of all materials, in a packaging field for high power microwave and milliwave communications requiring a high thermal conductivity and a multi-layer interconnection technique.
A diamond interconnection substrate according to the present invention includes diamond, and a conductive layer constituted by a presence of metal elements having a thickness of at least 10 nm and a concentration of at least 1020 cmxe2x88x921 in the diamond. More effectively, the conductive layer is constituted by the presence of metal elements having a thickness of at least 100 nm and a concentration of at least 1021 cmxe2x88x923.
To solve the problems described above, the diamond interconnection substrate of the present invention utilizes diamond having a thermal conductivity of approximately 2000 W/mK for the substrate, in which interconnections are provided within the diamond by implanting metal ions into the diamond substrate with a high energy level and a high dose.
Diamond is constituted by carbon atoms, each of which being a light element, and, different from Si and so forth, ions can enter very deeply into the diamond when implanted at a high speed. Further, fast ions (on the order of MeV) have a property in which a scattering cross section is small as long as the ions are at the high speed, so that they hardly collide with elements in a diamond crystal. Hence, the ions pass through the crystal without damaging the crystal. However, the scattering cross section is increased and the ions are rapidly stalled once the ions are decelerated in a substance, so that concentrated implantation is possible in a very narrow region.
Further, use of a mask enables forming of interconnections that are patterned together. That is, the interconnections can be formed with excellent controllability in depth and plane directions. It is also possible to attain a density value in the diamond very close to a density of metal, with a practical implant dose. This means that transfer of a substance, other than simple doping of elements into the diamond is possible.
Further, in a case that a conventional substance is used as a substrate material, when ions are implanted, energy of implanted elements may locally increase temperature and pressure of the material originally constituting the substrate, which may destroy the material. On the other hand, diamond has a high thermal conductivity such that it is hard to be heated to a high temperature, and also is very strongly bonded so as not to be destroyed.
Therefore, implantation of fast metal ions into the diamond substrate can produce an electrical interconnection area or areas within the diamond.
The diamond may be a monocrystal or a polycrystal, and either will have almost the same effect. Further, the effect described above can be attained even if an impurity is present in the diamond, since no doping is performed.
Further, interconnections are provided within the diamond, so that no gap can be formed between the diamond and the interconnections, and thus the interconnections cannot be corroded nor oxidized by acid or a severe environmental atmosphere. Thus, corrosive metals of alkali metals or alkaline earth metals may be utilized for the interconnections. It is understood that refractory metals of W, Mo, Nb, Pt and Ir may also be used. Lighter elements such as Li and Na of the metal elements can be implanted deeper, thereby causing less damage to the diamond.
Further, since the diamond substrate has a high thermal conductivity, heat of the metal interconnection is readily dissipated, so that even a low melting metal material has an electrical power transmission capability.
Preferably, the diamond interconnection substrate includes a plurality of conductive layers, the plurality of conductive layers being disposed at different depth positions with various distances from a surface of the diamond.
This can realize a multi-layer interconnection structure, facilitates arrangement of interconnections, and also realizes integration.
Preferably, in the diamond interconnection substrate, the plurality of conductive layers are electrically connected with each other in the diamond.
This allows each conductive layer to be electrically connected with each other.
Preferably, the diamond interconnection substrate further includes at least one electrode formed on the surface of the diamond, and at least one of the plurality of conductive layers is electrically connected to the at least one electrode.
This enables the conductive layers to be electrically connected to other circuit elements through the electrode.
Preferably, in the diamond interconnection substrate, the metal elements constituting the conductive layer are metal elements of at least one species selected from a group consisting of Cu, Ag, Au, Pt, Mg and Al.
Thus, a material can be selected as appropriate, and a low-melting/low-resistant material can be used to form the interconnections.
A method of manufacturing a diamond interconnection substrate according to the present invention includes the step of ion implanting metal elements with energy of at least 1 MeV and a dose of at least 1016 cmxe2x88x922 into diamond to form a conductive layer constituted by at least one metal element.
According to the manufacturing method of the diamond interconnection substrate of the present invention, the conductive layers that are to be interconnections can be formed within the diamond as described above, by ion implantation with the high energy (at least 1 MeV) and the high dose (at least 1016 cmxe2x88x922).
Preferably, in the method of manufacturing a diamond interconnection substrate, the ion implanting is performed a number of times by varying implantation depths of the metal elements into the diamond.
Implantation at different implantation depths can provide various arrangement positions and shapes of the conductive layers.
The implantation depth can be changed by varying implantation energy. For example, if Cu ions are implanted with various energy levels such as 8 MeV, 6 MeV and 4 MeV, profiles of Cu ions implanted in respective implantation processes are partly overlapped with each other and are stacked in the depth direction.
Alternatively, the implantation depth can be varied even with a constant energy, by disposing an interposition somewhere in an ion implantation path. For example, there is a method of implanting ions in multiple stages, in which ions are first implanted with the energy level of 8 MeV without any interpositions in the implantation path. Thereafter ions are implanted with a thin (100 to 200 nm) metal layer interposed somewhere in the implantation path. Then, ions are further implanted with a thicker metal layer interposed in the implantation path. In such a case, the interposition metal layers serve as decelerating layers for the implantation, which effectively varies the energy level of the implantation ions in the diamond, resulting in various implantation depths. This allows the profiles of Cu ions implanted in respective stages to be partly overlapped with each other and stacked in the depth direction.
Alternatively, the implantation depth can also be varied by changing ion species to be implanted, even with the same energy level. For example, when Al ions are implanted with 5 MeV and Cu is implanted with 8 MeV, the respective profiles of Al ions and Cu ions are overlapped with each other. When the implantation profiles are thus overlapped, a width of the implantation region in the depth direction will be thicker compared to that of a single implantation profile alone, and further a resistance value of the implantation region will be lowered. Thus, implantation of different ion species can control the thickness of the conductive layers.
Preferably, in the method of manufacturing a diamond interconnection substrate, profiles of the metal elements implanted by several ion implanting steps are overlapped with each other while being stacked in a depth direction to form a single conductive layer.
As described above, by changing the implantation depth for each ion implantation in a plurality of ion implantation steps, it will be possible to stack the profiles of metal elements implanted in the respective implantation steps in the depth direction.
Preferably, in the method of manufacturing a diamond interconnection substrate, profiles of the metal elements implanted by several ion implanting steps are disposed at different depth positions without overlapping with each other, to form a plurality of conductive layers divided in multiple layers.
For example, profiles will not be overlapped when energy levels of 8 MeV and 2 MeV are used to implant Cu, or when 6 MeV is used to implant Al and 4 MeV is used to implant Cu. Thus, implantation depth can be controlled. Further, a method in which at least 1 xcexcm of diamond is formed on an implantation surface by a vapor synthesizing process after one implantation step and thereafter a further implantation step is performed, can be used to form profiles without an overlap (even when the implantation is performed under the same condition). By repeating this once or more than once, arbitrary multi-layered conductive layers can be formed. Further, multi-layer interconnections having arbitrary shapes can also be performed by using masks having different patterns for the respective implantation steps. As such, fabrication of a multi-layer interconnection substrate having an interconnection of an arbitrary shape at an arbitrary interlayer is enabled. Further, the method of controlling the thickness of the conductive layers described earlier can be used to form conductive layers having arbitrary thicknesses at arbitrary layers.
Moreover, if the energy level is changed in a fairly large range and implant ion species are also changed by the method of controlling the thickness of the conductive layers described earlier, the conductive layers can have the thickness ranging from a predetermined depth position to the surface. This method can be utilized for extracting an electrode to the top surface and for forming an electrode connection between metal layers.
It is noted that the implantation, deposition or embedment of a metal layer into a through hole formed after formation of the multi-layer interconnection, also enables a connection between layers and extraction of an electrode to the top surface.
Preferably, in the method of manufacturing a diamond interconnection substrate, at least the implanting energy of the ion implanting or the type of the metal elements is changed to vary an implantation depth of the metal elements in the ion implanting.
This enables formation of conductive layers having different widths (thickness) in the depth direction and formation of a multi-layer interconnection structure, as described above.
Preferably, the method of manufacturing a diamond interconnection substrate further includes the step of synthesizing a diamond layer on a surface of the diamond by a vapor synthesizing process, and the step of ion implanting the metal elements and the step of synthesizing the diamond layer after the ion implanting steps have been repeated to form a multi-layered conductive stack in which the individual layers are disposed on planes different from each other.
Through the characteristics as described above, the present invention allows synthesis of diamond at approximately 1000xc2x0 C. over the substrate after provision of the interconnections. Thus, by repeating the step of ion implanting metal elements and the step of synthesizing the diamond layer, the total number of the multi-layer interconnections can almost be infinity, and a low melting/low resistivity material (Al, Ag, Au and Mg) can be used for the interconnection metal.
Preferably, in the method of manufacturing a diamond interconnection substrate, a mask layer formed on a surface of the diamond is patterned using a photolithography process, and the ion implanting is performed on the diamond through the patterned mask layer, to form the conductive layer of a predetermined shape.
This enables two-dimensionally controlled patterning by the mask.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.